1. Field of the Invention
This invention relates to a video data recording and/or reproducing apparatus and more particularly to an arrangement highly suited for a video data recording and/or reproducing apparatus wherein the picture change-over portion of the video data in one recording track differs from the position obtained in another track.
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows in outline the typical arrangement of the conventional digital video tape recorder (hereinafter referred to as DVTR). The recording operation of the DVTR is as follows:
Referring to FIG. 1, an input image signal is converted into digital data by an analog-to-digital (hereinafter referred to as A/D) converter 30. Redundant data is removed by an encoder 31 by utilizing correlation between images. Next, an error correction code (ECC) is added by an ECC encoding circuit 32 to the digital data against occurrence of any error relative to the recording medium. Further, a modulator 34 performs a digital code modulating action to obtain a signal spectrum distribution suited for magnetic recording and reproduction. Then, the output of the modulator 33 is recorded on a magnetic tape 36 through a magnetic head 35.
In reproducing, the video data recorded on the magnetic tape 36 is reproduced through a reproducing head 37, a head amplifier 38 and a digital demodulator 39. The signal in this stage includes some code error relative to the recording medium (tape), as mentioned above, such an error resulting from dust, a flaw or the like. Therefore, the error is corrected by an ECC decoding circuit 40. After that, redundant information such as a synchronizing (hereinafter referred to as sync) signal is added and the input information is nearly completely restored to its original state by a decoder 41. Lastly, a digital-to-analog (hereinafter referred to as D/A) converter 42 converts the digital signal into an analog image signal which is similar to the input image information.
Many DVTRs of the kind described have recently been developed. FIG. 2 shows a recording track pattern formed by these DVTRs. As shown, one picture plane is formed with a plurality of tracks in general. For example, the video signal of a first field is recorded in the tracks T1 to T3 and the video signal of a second field in the tracks T4 to T6.
Generally, the number of tracks to be formed by the video signal of one field is arranged to be an even number, because this arrangement is advantageous in respect to the synchronized operation of the DVTR, concatenated recording, editing, variable speed recording, etc.
During recent years, the technology for encoding video data with a high degree of efficiency has made a rapid advancement mainly in the communication field for TV conference systems, TV telephone system, etc.
Meanwhile, a demand for a longer recording time of DVTRs has increased. The length of recordable time of the DVTR can be increased by using the high efficiency image encoding technique developed in the field of communication technology. The technique will likely come to be actively applied to the DVTR for this purpose.
However, an attempt to record data which is further compressed through a high efficiency encoding process with the highest possible degree of density would encounter a problem that the picture change-over position of the video data within a recording track on the recording medium tends to fluctuate and vary from that of another track. In such a case, it is difficult to have the video data received and produced in units of fields or frames. This would make it difficult to carry out the above-stated synchronized operation of the DVTR, concatenated recording, editing work, etc.
In a case that some video data is newly recorded by such a DVTR on a recorded tape, it is inevitable to have a picture having a drop-out part in its data. This does not mean simple drop-out of some picture elements within a picture but might make impossible the reproduction of all the picture elements of the picture, because the DVTR is generally arranged to utilize the correlation among picture elements of one and the same picture plane for the purpose of compressing the data. Further, even if only a reproducible picture can be extracted, it is impossible to adequately match the reproduction timing of one picture with that of another at the concatenating part between them. Therefore, adequate reproduction is hardly expectable under such a condition.
Further, if the data of such an imperfect picture remain on the tape, it would be impossible to reproduce any adequate picture from the tape. In other words, the video data becomes discontinuous as no image can be obtained from the data of the imperfect picture. This discontinuity of video data would result in a conspicuous skew or a skipped picture appearing at a concatenated part of the record. In this instance, even if some time code is recorded longitudinally on the tape, it becomes impossible to correlate the time code with the video data recorded in oblique tracks. As a result, it is impossible to locate a picture being looked up by finding its record ranging from a point in one track to a point in another. A quick look-up is difficult under such a condition.
This problem may be solved by recording one field or frame portion of the video data in an even number of tracks without fail. This method, however, hinders efforts to increase the recording density, because assuming that one field amount of video data is successfully compressed to be recordable in 2.1 tracks by the record density increasing efforts, this method still requires three tracks for one field amount of the video data.